Nonvibratory electric switch



1970 s. 1. GREENE NONVIBRATORY ELECTRIC SWITCH Filed Oct. 14, 1968VISCOUS FLUID FIG.

us. Cl. 200-43 United States Patent O ABSTRACT OF THE DISCLOSURE v Anonvibratory electric switch comprises a fixed contact element, amovable contact element in the form of a resilient leaf spring fixed atone end and engageable with the fixed contact element at its other endbut normally in circuit-open position. A member for actuating themovable contact element to circuit-closing position is in the form of afluid pressure-responsive device subject to vibration. A guide isinterposed between the pressureresponsive device and the movable contactelement and includes a guide surface in the form of a cylindrical boreextending therethrough. An actuating element in the form of a pinloosely fitting in the bore normally engages, but is movableindependently of, the actuating member. A viscous fluid fills the spacebetween the bore and the actuating pin and is effective to dampvibrations of the latter, whereby the switch contact elements areeffectively isolated from vibratory movements of the actuating member.

BACKGROUND OF THE INVENTION This invention relates to nonvibratoryelectric switches and particularly to such switches of the type adaptedto be actuated by a fluid pressure-responsive device subject tovibration which, in the absence of the invention, causes the contacts tochatter when the device is set so that the range of control movementapproaches the amplitude of vibration. The electric switch of theinvention has been found particularly useful in precision controlequipment that must operate within close pressure bands under severevibration.

A conventional prior fluid pressure-responsive electric switch hascomprised a fixed contact element and a movable contact element eithersecured to, or actuated directly by, the pressure-responsive device,usually in the form of a pressure capsule, bellows, diaphragm, or thelike. If it is desired to actuate the switch in response to relativelysmall changes in pressure and if the device is subject to vibration, itfrequently occurs that the range of control movement of the actuatingpressure-responsive device becomes of the same order as the amplitude ofits vibratory movement, causing the switch contacts to chatter, that is,to open and close at the vibratory frequency.

SUMMARY OF THE INVENTION In accordance with the invention, there isprovided a nonvibratory electric switch comprising a fixed contactelement, a movable contact element including a resilient member normallyholding the same in a predetermined relation to the fixed element, and amember for actuating the movable element to a diiferent relation to thefixed element, such member being subject to vibration. The electricswitch of the invention also comprises a guide interposed between theactuating member and the movable element and including a cylindricalbore extending therethrough and a pin disposed in the bore with aclearance of the order of 0.0003 inch and normally engaging theactuating member. A fluid having a viscosity of the order Patented Nov.3, 1970 of 5000 cs. fills the space between the cylindrical bore and thepin and is effective to damp vibrations of the latter, whereby thecontact elements are effectively isolated from vibratory movements ofthe actuating member.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription, taken in connection with the accompanying drawing, whileits scope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a cross-sectional view of a nonvibratory electric switchembodying the invention;

FIG. 2 is a diagrammatic representation of the operation of a prior artswitch of the type described, while FIG. 3 is a similar diagramrepresenting operation of an electric switch embodying the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of thedrawing, there is represented in cross-section a nonvibratory electricswitch comprising a cup-shaped housing 10, the open end of which isclosed by a threaded plate 11 engaging internal threads 10a of thehousing 10. Mounted in the plate 11 is a fixed contact element 12secured to a terminal 13. A movable contact element is in the form of aresilient leaf spring 14 fixed at one end to a terminal 15 and the otherend being engageable with the fixed contact element 12, the contactelements 12 and 14 being normally open, as shown.

The electric switch of the invention further comprises a member foractuating the movable element 14 to a different relation to the fixedelement 12, specifically to circuit-closing position. The actuatingmember is shown in the form of a fluid pressure-responsive device,specifically a bellows 16 having a fluid connection through a port 17extending through the lower wall of the housing 10. A guide isinterposed between the actuating bellows 16 and the movable contactelement 14 in the form of a bushing 18 secured to or integral with theplate 11 and including a guide surface in the form of a cylindrical borethrough the bushing 18. In the bore of the guide 18 is disposed anactuating element in the form of a loosely fitting pin 19. The pin 19normally engages the upper face of the bellows 16 but merely reststhereon so that it is freely disengageable therefrom.

In the electric switch of the invention, the space be tween the guidesurface or bore in the bushing 18 and the actuating pin 19 is filledwith a viscous fluid which is retained solely by capillary attraction.This viscous fluid is effective to damp vibrations of the actuating pin19, whereby the contacts 12, 14 are effectively isolated from vibratorymovements of the actuating bellows 16.

The operation of the electric switch of the invention in comparison withconventional prior electric switches of a similar type is shown in FIGS.2 and 3. In FIG. 2, the upper face of the bellows 16 is shown aspartaking of a sinusoidal vibratory movement, represented by curve A. Inits uppermost position, the bellows, acting through the conventionalpin, close the switch contacts as shown. In the lowermost phase of itsvibratory movement, the bellows cause the pin to retract with thebellows, either by being secured to the bellows or by falling of its ownWeight, thereby permitting the switch contacts to open, as illustrated.This cycle is repeated, as shown in the two succeeding maximum andminimum of the vibratory curve A. The pin is shown as sliding in a guidemerely to restrict its lateral movement.

Turning now to FIG. 3, it is assumed that the bellows still partake ofthe same sinusoidal vibratory movement represented by curve A. In thisinstance however, the actuating pin is damped by the viscosity of theoil filling the space between the bore of the bushing 18 and the pin sothat, when the bellows reach their minimum position on curve A, the pinis restrained from downward movement, maintaining the contacts closed.This cycle is repeated, as shown with respect to the two succeedingphases of the sinusoidal curve A.

It has been found that the clearance between the pin 19 and the "bore ofthe bushing 18 may the of the order of 0.0003 inch and that theviscosity of the fluid may have a value of the order of 5000 cs. In oneembodiment of the invention which has proved satisfactory, the clearancebetween the pin 19 and the bore of the bushing 18 was of the order of0.0003 inch and the fluid was silicone oil having a viscosity value ofthe order of 5000 cs. In the embodiment of the invention described, therange of amplitude vibration was up to $0.20 inch and the range ofvibration frequencies effectively clamped by the construction describedwas from to 2000 cycles per second.

While there has been described what is, at present, considered to be thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein, without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A nonvibratory electric switch comprising:

a fixed contact element;

a movable contact element including a resilient member normally holdingthe same in a predetermined relation to said fixed element;

a member for actuating said movable element to a different relation tosaid fixed element, said member being subject to vibration;

a guide interposed between said actuating member and said rnovaJbleelement and including a cylindrical 'bore extending therethrough;

a pin disposed in said bore with a clearance of the order of 0.0003 inchand normally engaging said member;

and a fluid having a viocosity of the order of 5000 cs. filling thespace between said cylindrical bore and said pin effective to dampvibrations of the latter, whereby said contact elements are eifectivelyisolated from vibratory movements of said actuating member is effectiveto close the same.

2. A nonvibratory electric switch in accordance with claim 1 in whichsaid contact elements are normally open and said actuating member iseffective to close the same.

3. A nonvibratory electric switch in accordance with claim 1 in whichsaid resilient member is in. the form of a leaf spring fixed at one endand engageable with said fixed contact element at its other end.

4. A nonvibratory electric switch in accordance with claim 1 in whichsaid actuating member is afluid pressure-responsive device.

5. A nonvibratory electric switch in accordance with claim 1 in whichthe viscous fluid is a silicon oil.

References Cited UNITED STATES PATENTS 2,149,068 2/1939 Paul et a1.

2,445,756 7/ 1948 Bean.

2,579,717 12/1951 Wood.

2,589,025 3/1952 Phelps et al. v 2,939,928 6/1960 Learn. 1 3,296,9891/1967 01th et a1. 112-256 3,365,557 1/ 1968 Cooper et al. 200-833,378,656 4/1968 Johnson.

1 ROBERT K. SCHAEFER, Primary Examiner J. R. SCOTT, Assistant ExaminerU.S. Cl. X.R-

